1. Field of the Invention
The present invention relates to a rolled plate joining apparatus for joining the tailing end of a preceding rolled plate and the leading end of a succeeding rolled plate while traveling with the rolled plates in a hot rolling plant and to a continuous hot rolling apparatus equipped with the same.
2. Description of the Related Art
In conventional hot rolling plants (hot strip mills), bar materials rolled by a roughing mill are supplied separately to a finishing mill to obtain strip materials having a desired thickness. By such a means, however, all the rolled plates are not rolled uniformly, and, therefore, such problems as defects of leading ends and tailing ends are liable to occur, thereby lowering the yield of the rolled plates; and it is hard to increase the rolling speed due to such defects.
To solve the above problems, there are conventionally suggested joining apparatuses for joining the tailing end of a preceding rolled plate and the leading end of a succeeding rolled plate so as to supply the rolled plates to a finishing mill successively (e.g., Japanese Unexamined Patent Publication Nos. 62-252603 and 63-93408 and Japanese Patent Publication No. 5-139).
In the above-described rolled plate joining apparatuses, however, there are such problems as (1) the automation (mechanization) is difficult and the joined sections cannot be rolled uniformly, (2) since it takes a long time to weld wide rolled plates, the overall length of the plant is apt to be long, and (3) it is difficult to secure a satisfactory joined strength throughout the width of the rolled plates.
Therefore, the inventors of the present invention thought out a rolled plate joining apparatus capable of joining rolled plates with a satisfactory joined strength throughout the width in a short period of time and filed applications thereon (e.g., Japanese Unexamined Patent Publication No. 8-10809).
FIG. 1 is an example of a rolled plate joining apparatus made by the inventors of the present invention.
This rolled plate joining apparatus is equipped with a truck 3 that travels in the rolling direction, tailing end pinch rolls 4 that are mounted on the truck 3 and can be moved vertically with the tailing end of a preceding rolled plate 1 pinched horizontally, leading end pinch rolls 5 that are mounted on the truck 3 and can pinch horizontally the leading end of a succeeding rolled plate 2, machining apparatuses 6 for cutting the undersurface of the tailing end of the preceding rolled plate 1 and the upper surface of the leading end of the succeeding rolled plate 2, and a pressure welding apparatus 7 for joining the preceding rolled plate 1 and the succeeding rolled plate 2 with the machined surfaces of the preceding rolled plate 1 and the succeeding rolled plate 2 overlapped and reduced approximately to the thickness of the rolled plates 1 and 2.
Further, as is shown in FIGS. 2a and 2b, the rolled plate joining apparatus of Japanese Unexamined Patent Publication No. 8-10809 is equipped with the truck 3 that travels with apparatuses mounted thereon, a tailing end clamping apparatus 9 that can be moved vertically between a machining level H and pressure welding level L by an elevating apparatus 8 with the tailing end of the preceding rolled plate pinched horizontally, a leading end clamping apparatus 10 for pinching and holding the leading end of the succeeding rolled plate 2 at a pressure welding level L, a machining apparatus 11 for cutting simultaneously the undersurface of the tailing end of the preceding rolled plate 1 and the upper surface of the leading end of the succeeding rolled plate 2, a reduction keeping apparatus 12a for keeping the surfaces to be cut in a reducing atmosphere, and a pressure-welding apparatus 12b for pressure-welding the overlapped sections.
The machining apparatus 11 is composed of a conical cutter 13 that is rotated about an axis X slanted to the level and a transverse moving apparatus 14 for moving horizontally the conical cutter 13 throughout the width of the rolled plates from a position that is out of the position of the rolled plates. The conical cutter 13 has a pair of truncated conical surfaces 13a, 13b whose tops are directed outward and the uppermost part and the lowermost part of the truncated conical surfaces are generally horizontal, so that the uppermost part and the lowermost part of the truncated conical surfaces can touch the undersurface of the tailing end and the upper surface of the leading end simultaneously respectively. In passing, cutter tips 13c are embedded in the truncated conical surfaces 13a, 13b. Further, 15a indicates a traverse moving table of the traversing apparatus 14.
Further, Japanese Unexamined Patent Publication No. 7-214104 describes a hot rolling plant wherein joining machine is used. As is shown in FIG. 3 of the present application, this hot rolling plant is provided with a sizing press 16b on the exit side of a heating furnace 16a, and the leading end and the tailing end of a rolled plate 1 rolled by a roughing mill 16c provided on the exit side thereof is sheared by a crop shear 16d. The tailing end of the sheared preceding sheet bar and the leading end of the sheared succeeding sheet bar are joined by a fuse-joining apparatus 17 and are subjected to finish rolling by a group of finishing mills 16e and the joined sheet bars are wound by a winding machine 16f.
(1) In the rolled plate joining apparatus shown in FIG. 1 or 2 of the present application, it is required to align the center lines of the preceding rolled plate 1 and the succeeding rolled plate 2. FIG. 4 shows a state wherein the center line of one rolled plate is not aligned with the center line of other rolled plate to be joined and if they are joined in this state, plate breaking or camber due to the defective joining will occur. FIG. 5 of this application shows misalignment of the center lines in the joined sections of rolled plates having different widths. If the center line of a preceding rolled plate and the center line of a succeeding rolled plate are misaligned in this way, problems arise that will cause serious troubles with succeeding finishing rolling or the like.
(2) Further, the life of the conical cutter 13 of the rolled plate joining apparatus shown in FIG. 2 of the present application is extremely short due to such factors as [1] the conical cutter 13 is exposed to a high-temperature atmosphere by the reduction keeping apparatus, [2] the conical cutter 13 is rotated at a high speed by the driving apparatus, [3] the conical cutter 13 is moved horizontally in the width direction of the rolled plates by the traverse moving apparatus, and [4] use of the cutter tips for the conical cutter makes the heat capacity small. In addition, it is difficult to provide a cooling mechanism, because, for example, [1] the driving apparatus is attached to the extremity of the shaft of the conical cutter and [2] a key groove into which a key is fitted is formed in the inner circumferential surface of the conical cutter.
(3) Furthermore, in the rolled plate joining apparatus, the cutting of the surfaces to be joined is required to be done in a short period of time. Because, if the cutting time becomes long, the joining time becomes long, which makes the traveling distance of the joining apparatus long and therefore the rolling line becomes long. Furthermore, since the surfaces to be cut during the cutting are covered with reducing flames to prevent them from being oxidized, the surfaces to be cut are at a high temperature and therefore a lubricant cannot be used during the cutting. As a result, the cutter tips are abraded intensely, the life thereof is short, and therefore the cutter has to be replaced frequently. Further, if the cutter is damaged during the cutting, the replacement takes a longer time, and during that time, the joining operation and the rolling operation have to be stopped. The joining is carried out with a certain interval between the joining operations, but the heat capacity of the cutter is large, the cutter tips are not cooled in many cases until the next joining operation, and therefore the temperature of the cutter tips during the cutting is increased to make the life short.
(4) Furthermore, in the hot rolling plant shown in FIG. 3 of the present application, since the rolled plates after the rough rolling are not wound, the rolling line becomes long. Then, in this plant, the temperature of the rolled plates supplied to the finish rolling machine is lowered and the finish rolling cannot be carried out suitably in many cases. Furthermore, in many cases, the joined sections bulge in the plate width direction, and this bulge is expanded by rolling in the succeeding step. FIG. 6 herein shows the shape of the bulge at the joined sections. The plate width at the joined position of the rolled plate 1 has a bulge 1a. In FIG. 7 of this application, the rolled plate 1 is tapered at the opposite ends to form edge drops 1b. Edge drops 1b cannot secure the precision of the plate thickness at the opposite ends and therefore are trimmed, resulting in a decrease in the yield. The plant shown in FIG. 3 does not have a correcting apparatus for correcting such joined sections or a defective thickness at the opposite ends due to rolling. Furthermore, since there is no shear before the winding machine, it is required to sever the rolled plates for every quantity of the rolled plates that can be wound by the winding machine and the ability capable of operating continuously by the joining machine is not used. In passing, Japanese Unexamined Patent Publication No. 7-24503 discloses a post-forming machine for removing defective parts due to joining positioned on the exit side of a joining machine, but this post-forming machine cannot correct edge drops resulting from finish rolling.